Oligo(p-phenylene)s with a donor phenol group and an acceptor pyridinium moiety separated by one and two p-phenylene units were synthesized by the linear iterative Suzuki–Miyaura coupling method using aryl nonaflates as effective coupling reagents. Zwitterionic forms of these push–pull molecules were generated upon deprotonation of the phenol leading to large redshifts in absorbance maxima. UV-vis absorbance studies also revealed strong dependence of the band position on solvent polarity: a smooth bathochromic shift can be observed with the decrease of the solvent polarity. The molecule with one p-phenylene bridging unit showed the strongest solvatochromic characteristics in the series, spanning the range of 167 nm while moving from polar water to less polar N,N-dimethylformamide. The magnitude of this shift was close to Reichardt's dye — one of the most solvatochromic organic dyes known.
A novel β‐diketone ligand bearing a thiophene moiety and an anchoring Ph‐COOCH3 unit has been designed, prepared and used in synthesis of cyclometalated benzimidazole‐based iridium(III) complexes for application in dye‐sensitized solar cells (DSSC). The replacement of traditional 4,4'‐dicarboxy‐2,2'‐bipyridine by this aromatic β‐diketone results in excellent tuning the redox potentials and excited state properties of these IrIII complexes, one of which exhibits good efficiency when used as a dye in DSSC. All the complexes demonstrate reversible redox behavior, with oxidation potentials (Ir4+/Ir3+) strongly depending on the electron‐donor/withdrawing nature of the substituents in the cyclometalated ligands. Surprisingly, the latter has just a little effect on their luminescence spectra, in which structured emission bands are observed. Time‐resolved spectroscopic studies in combination with DFT calculations show that the complexes emit light by mixed 3MLCT–3LC excited states predominantly composed of the diketone ligand‐centered triplet state.
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